Many direct current to direct current (DC-to-DC) converters make use of the “buck” or the “multi-phase buck” topology. These topologies are illustrated in FIG. 1. In a single or multi-phase buck converter 100, a switching device 102 repeatedly couples a driven end of an inductor 104 to an input power source 106 at a given frequency referred to as the converter's switching frequency. This coupling causes a current to build up through inductor 104 between a converter output 108 and power source 106. When switching device 102 opens, inductor current continues to flow for a time, typically through either or both of a diode 110 and a second switching device 112, and thence into a load 114. If second switching device 112 is a transistor, diode 110 may be a body diode of the transistor. Accordingly, inductor 104 may be referred to as an energy storage inductor, and diode 110 and second switching device 112 couple energy stored in inductor 104 to load 114. A bypass or filtering capacitor 116 is typically provided to reduce ripple by smoothing voltage provided to load 114, and an input capacitor 117 is typically coupled across input power source 106 to supply the converter's ripple current requirements. A variable-resistor symbol is used to represent load 114 because effective load resistance may change during operation. Voltage provided to the load 114 and/or another converter parameter is typically sensed by a controller 120 that provides for control and drive of the switching devices 102 and 112; for simplicity of illustration connections between controller 120 and switching devices are not shown. The switching devices are selected by a designer from transistors deemed to be good for switching regulators such as MOS (including CMOS & LDMOS), Gallium Arsenide and Bipolar transistors, and such other electronic switching devices such as gate-turnoff thyristors as known in the art of electronics.
In order to provide for high current capability and reduce ripple, one or more additional phases may be provided to extend the design into a multi-phase converter design, where each phase adds an additional switching device, such as switching device 122, diode 124 and/or second switching device 126, and inductor 128 to the design. These switching devices 122, 126 also operate under control of controller 120, and are typically timed to reduce ripple such that device 122 and device 102 do not turn on simultaneously, although they both may be on simultaneously. The timing relationship between turn-on of devices 122, 102 within a converter cycle is a phasing, or a phase relationship between the primary and additional phases of the multi-phase converter.
Multi-phase DC-to-DC converters may be designed without magnetic coupling between the inductors 104 and 128 of different phases, or may be designed with specific coupling between the inductors of different phases as described in U.S. Pat. No. 6,362,986 to Schultz, et al., the disclosure of which is incorporated herein by reference.
Multi-phase DC-to-DC converters can be used in many applications including digital and analog IC chips, such as to provide bias power supplies for the chips. One challenging example is for a power supply to high performance microprocessors. Modern processor integrated circuits often require very low operating voltages, such as voltages at predetermined levels from around one to two and a half volts, and may require very high currents of as much as hundreds of amperes. Further, these processors are often designed with power-saving circuitry that can save considerable power by disabling functional units when those units not needed, but can cause current demand to soar dramatically over very short periods of time as functional units within the processor are enabled when needed. For example, current demand by some processors may jump by at least 100 amperes within a microsecond, effective load 114 resistance changing sharply between values in the ranges of ohms or tenths of ohms and values on the order of less than a hundredth of an ohm. These processors therefore impose stringent requirements on their associated power supply systems. Typically, these processors are powered from five or twelve volt power supplies thus requiring step-down DC-to-DC converters such as multi-phase buck converters, and large filtering capacitors 116 are provided to allow for load current changes.
Many DC-to-DC converter applications require a voltage step-up rather than the step-down provided by the buck converter of FIG. 1. Many other architectures for single and multiple-phase converters exist that can meet such requirements.
Among those DC-to-DC converter architectures that are capable of providing a voltage step up, the most common is the boost converter, single-phase boost converters have been used for many years in such applications as powering the cathode-ray tube of television receivers. FIG. 2 illustrates a multi-phase boost converter 200, having an inductor 202, 204 associated with each phase. Each phase also has at least one switching device, represented by switch 206, and a diode 208. A second switching device, represented as switch 210, may be provided to bypass forward voltage drop of the diode 208; diode 208 and switch 210 together couple energy from inductor 202 to load filter capacitor 212 following each turnoff of switch 206. A controller 214, which may operate under feedback control by sensing load voltage and/or another converter parameter, is provided for driving switching devices 206, 210.